1,4-dioxane is a cyclic ether expressed by the following formula (1). 1,4-dioxane is excellent in compatibility with water or organic solvent and is usually used as a reaction solvent for organic synthesis.

The manufacturing and import volume of 1,4-dioxane in Japan in 2010 was about 4500 t/year and it is presumed that 1,4-dioxane is released into the environment by about 300 t/year. 1,4-dioxane is water-soluble, and thus 1,4-dioxane diffuses over a wide area when it is released into a water environment. Also, 1,4-dioxane is inferior in volatility, adsorption to solids, photodegradability, hydrolyzability, and biodegradability, and thus it is difficult to be removed from water. Since 1,4-dioxane has acute toxicity and chronic toxicity, and further, carcinogenicity is indicated, the contamination of water environments by 1,4-dioxane is considered to adversely affect humans and animals and plants. Therefore, in Japan, 1,4-dioxane is regulated by a tap water quality standard (0.05 mg/L or less), an environmental standard (0.05 mg/L or less), and a wastewater standard (0.5 mg/L or less).
It is not possible to sufficiently remove 1,4-dioxane from water by conventional treatment methods such as the activated sludge method and the activated carbon adsorption method. The effectiveness of 1,4-dioxane treatment is confirmed only in the advanced oxidation processes using a plurality of physicochemical oxidation methods such as an ozone treatment (O3/H2O2) with addition of hydrogen peroxide, an ozone treatment (O3/UV) under ultraviolet irradiation, an ozone treatment under irradiation with radiation or ultrasonic wave in combination. However, the accelerated oxidation method is not widely used due to the high initial cost and running cost. Furthermore, in Non-Patent Literature 1, it is reported that the efficiency of 1,4-dioxane treatment by the accelerated oxidation method decreases when an organic substance other than 1,4-dioxane is present.
There is a demand for a method for treating water containing 1,4-dioxane stably at a low cost, and a biological treatment by 1,4-dioxane-degrading bacteria is proposed in Patent Literature 1 and Non-Patent Literature 2.
1,4-dioxane-degrading bacteria are roughly classified into two groups of bacteria (assimilation bacteria) that can decompose and assimilate 1,4-dioxane as a single carbon source and bacteria (co-metabolizing bacteria) which decomposes 1,4-dioxane by co-metabolic reaction in the presence of other components such as tetrahydrofuran. Assimilation bacteria are further classified into inducible type and constitutive type depending on whether 1,4-dioxane-degrading enzyme is induced by specific substrates or not. In Non-Patent Literatures 3 and 4, it is reported that the THF monooxygenase possessed by these 1,4-dioxane-degrading bacteria are involved in the degradation of 1,4-dioxane. THF monooxygenase is classified as one type of soluble iron (II) monooxygenase (SDIMO) which is responsible for the initial oxidation of various hydrocarbons. Methane/propane monooxygenases and the like are contained in SDIMO (Non-Patent Literature 5). Furthermore, in Non-Patent Literature 6, it is reported that bacteria having SDIMO other than THF monooxygenase can also decompose 1,4-dioxane.
1,4-dioxane-degrading bacteria are extremely slow to proliferate, and when other microorganisms are intermixed, other microorganisms preferentially proliferate. Thus, in order to cultivate 1,4-dioxane-degrading bacteria, it is necessary to sufficiently sterilize the culture apparatus and the medium beforehand so that other bacteria are not intermixed. For sterilization treatment, there are methods such as steam sterilization using an autoclave, dry heat sterilization by heating in an oven or the like, radiation sterilization using gamma rays, and chemical sterilization using ethylene oxide gas. However, since, equipment for sterilization is extremely large scale, energy cost is extremely high, and there is a problem in terms of cost and safety in that the amount of chemicals to be used becomes large, any of the above sterilization methods are difficult to be performed on a large scale. Therefore, it is difficult to supply as much 1,4-dioxane-degrading bacteria as needed at the actual 1,4-dioxane pollution site.